The present preferred embodiment relates to devices for guiding an endless web as used for example in a printer or copier. The present preferred embodiment also relates to methods for guiding an endless web.
In the guiding of a paper web through a printer, non-uniform mechanical properties of the web or a basic setting of the various guide rolls that is not precisely parallel can result in a lateral shifting of the paper web, and can cause the formation of waves in some areas and/or sagging at one side of the web, even if the front edge is running in a stable fashion. At points of deflection with counter-pressure or back pressure rolls, as are, for example, required for transport, such waves can be pressed to form folds. In addition, sagging at one side of the web, for example in the area of a fixing station that operates in contactless fashion, is disturbing, because the sagging web segment can come into contact with mechanical parts, so that the toner images are smudged, or the sagging segment is exposed to an excessively high energy load.
From U.S. Pat. No. 5,021,673, a device is known for guiding a paper web in which for the guiding of the web, rolls are situated at both lateral edges that exert pressure on the web with different forces. In this way, a lateral shifting of the web can be corrected.
In U.S. Pat. No. 5,323,944, a device for controlling the lateral position of a web is described with which the web is guided between a pressure roll and a counter-pressure roll. The pressure roll can be pivoted, and the force exerted on the counter-pressure roll along its shaft or axle can be varied in order to shift the side edges of the web. The current position of the side edges of the web is acquired using optoelectronic sensors.
U.S. Pat. No. 6,104,907 describes a device for guiding a paper web in a printer. In order to avoid vibrations and variations in speed, the web is guided around rolls and is clamped by them, which also counteracts a lateral shifting of the web. For example, in order to avoid lateral shifting, a guide roll is used having pins that engage in corresponding holes in the web. In another variation, the force that a roll exerts along its axis on the web is varied. In another variation, the web is guided between pairs of upper and lower rolls. These upper and lower rolls wrap and clamp the web with an enlarged wrap angle, thus preventing a variation in speed of the web.
From documents DE 689 07 466 T2, DE-OS 14 24 318, DE 195 20 637, and DE 199 60 649 A1, web guiding devices are known for guiding an endless web. In addition, pivotable draw-off devices for paper webs are known from DE 199 53 353 A1 and DE 44 35 077 A1.